In the formation of coupled polymers, an alkali metal- or alkaline earth metal-terminated polymer is treated with a multifunctional compound containing two or more reactive sites capable of reacting with the carbon-metal bonds of the alkaline earth- or alkali metal-terminated polymer. The multifunctional compound affords a nucleus for the resulting coupled polymer, producing a molecular structure possessing a nucleus from which radiate long-chain branches attached to the nucleus via the coupling reaction. Polymers derived from difunctional coupling agents are linear, while coupled polymers derived from coupling agents possessing three or more reactive sites are termed "radial polymers." Coupled polymers, particularly, the radial polymers, have been of particular value because of the improvements in Mooney viscosity, processability, and reduction in cold flow that these polymers exhibit relative to their respective parent uncoupled polymers.
Hydrogenation of such coupled polymers has received considerable attention, since removal of unsaturation within the rubbery polymers improves the polymer resistance to environmental attack, e.g., from oxygen and/or ozone. Effectiveness of the hydrogenation, and the value of the resultant hydrogenated polymer, inherently is dependent upon the reasonable completeness of the hydrogenation, otherwise significant degrees of unsaturation would remain available as points for degradative environmental attack. Contaminants that impede hydrogenation theoretically can be removed by repeated coagulation, recovery, purification by various means such as molecular sieves, redissolution and the like, of the polymer. These treatments can be expensive, and in themselves may introduce contaminants because of traces of oxygen, moisture and the like in the solvents used.
At the same time, improvements have been sought with regard to minimizing conditions, such as hydrogenation times, and the like. Minimizing exposure of the polymer to peak hydrogenation temperatures by minimizing hydrogenation times assists in avoiding breakdown of the polymer during hydrogenation, thus maintaining, as far as possible, benefits obtained from the increase in molecular weight, increased Mooney values, obtained through the coupling procedures.